1. Field of the Invention
The present invention generally relates to interlayers and laminates comprising a cellulose ester. More particularly, the present invention generally relates to structural interlayers and laminates comprising at least one layer that contains a cellulose ester.
2. Description of the Related Art
Generally, multiple layer glass panels comprise a laminate comprised of an interlayer or multilayer interlayer or interlayers sandwiched between two panes of glass. In some applications, a laminate may comprise only one pane of glass or other rigid substrate. The laminated multiple layer glass panels are commonly utilized in architectural window applications, in the windows of motor vehicles and airplanes, and in photovoltaic solar panels. The first two applications are commonly referred to as laminated safety glass. Typically, the main function of the interlayer in the laminated safety glass is to absorb energy resulting from impact or force applied to the glass, keep the layers of glass bonded even when the force is applied and the glass is broken, and prevent the glass from breaking up into sharp pieces. Additionally, the interlayer generally gives the glass a much higher sound insulation rating, reduces UV and/or IR light transmission, and enhances the aesthetic appeal of the associated window.
The interlayer is generally produced by mixing a polymer resin, such as poly(vinyl acetal), with one or more plasticizers and melt processing the mix into an interlayer by any applicable process or method known to one of skill in the art. After the interlayer or multilayer interlayer is formed, it is typically collected and rolled for storage and for later use in multiple layer glass panels.
Interlayers can be incorporated into multiple layer glass panels using various techniques known in the art. For example, at least one multilayer interlayer can be placed between two substrates and any excess interlayer can be trimmed from the edges, thereby creating an assembly. It is not uncommon for multiple interlayers to be placed within the two substrates thereby creating a multiple layer glass panel with multiple interlayers. Subsequently, air can be removed from the assembly by an applicable process or method known to one of skill in the art, e.g., through nip rollers, vacuum bag, vacuum ring, or another de-airing mechanism. Additionally, the interlayer can be partially press bonded to the substrates by any method known to one of ordinary skill in the art. In a last step, in order to form a final unitary structure, this preliminary bonding can be rendered more permanent by a high temperature and pressure lamination process known to one of ordinary skill in the art such as, but not limited to, autoclaving.
An emerging market in architectural laminated glass requires interlayers with structural properties such as load bearing ability. Such an interlayer is Eastman's Saflex™ DG, which is made of plasticized polyvinyl butyral (“PVB”). Generally, Saflex™ DG interlayers are stiffer products than standard PVB interlayers and this higher stiffness allows laminates made with Saflex™ DG interlayer to sustain higher loads. Alternatively, Saflex™ DG interlayers can be used to allow a reduction in the glass thickness while achieving the same laminate loading.
Consequently, higher performance interlayers are desirable as more applications requiring stiffer interlayers are emerging (e.g., single side balcony laminates, canopies, staircases, and support beams). However, many of the commercially-available PVB interlayers exhibit deficiencies in terms of processability and/or functionality. Further, the attraction of glass in many of these structural applications is the clarity of the glass panel. Thus, the PVB layers must also not hinder the optical properties of the structural glass articles in which they are incorporated.
Accordingly, there is a need for an interlayer for use in structural laminates that can provide the desired structural support and not compromise the optical properties of the laminate.